On 10/03/16 13:34, Emil Velikov wrote:
On 30 September 2016 at 18:26, Laszlo Ersek lersek@redhat.com wrote:
On 09/30/16 18:38, Hans de Goede wrote:
Hi,
On 30-09-16 17:33, Laszlo Ersek wrote:
On 09/30/16 16:59, Hans de Goede wrote:
Hi,
On 30-09-16 16:51, Laszlo Ersek wrote:
On 09/30/16 12:35, Hans de Goede wrote:
> Attached are 2 patches against the xserver which should fix this, > please give them a try.
Sorry about the delay.
The patches don't seem to fix the issue for me. Please see the Xorg log attached.
I tested the patches as follows. Given that my bisection had been done in a Fedora 24 guest, using
xorg-x11-server-1.18.4-4.fc24 http://koji.fedoraproject.org/koji/buildinfo?buildID=794494
I now rebuilt the guest kernel exactly at the failing commit (a325725 "drm: Lobotomize set_busid nonsense for !pci drivers"), and first reproduced the issue with the above X server.
Then, I ported your patches to "xorg-server-1.18.4" (using the upstream xserver tree), and rebuilt the Fedora package with the backport. For the backport, I had to cherry-pick the following two patches from master first:
1 ca8d88e50310 xfree86: recognize primary BUS_PCI device in xf86IsPrimaryPlatform() 2 ea91db4b8331 config: fix GPUDevice fail when AutoAddGPU off + BusID
This way your patches applied cleanly. (Cherry pick #1 above is actually necessary for semantics, while cherry pick #2 is needed for a clean context only, and has no impact for this test.)
That is, in total, I added the following four patches to the Fedora 24 package:
1 xfree86: recognize primary BUS_PCI device in xf86IsPrimaryPlatform() 2 config: fix GPUDevice fail when AutoAddGPU off + BusID 3 xfree86: Make adding unclaimed devices as GPU devices a separate step 4 xfree86: Try harder to find atleast 1 non GPU Screen
You can find the scratch build that I used for testing here:
xorg-x11-server-1.18.4-4.hans_bz1366842_2.fc24 http://koji.fedoraproject.org/koji/taskinfo?taskID=15875087
Another reason I used F24's X server as basis, rather than upstream HEAD, is that Fedora 24 is pretty young, and it's already on kernel 4.7.4, and I believe it will soon move to kernel 4.8, without (necessarily) rebasing its X server package to upstream. IOW the kernel upgrade to 4.8 will break X in Fedora 24 too, and then I expect the Fedora X maintainers would have to cherry pick those two patches as dependencies just the same.
To summarize, the patches don't seem to help. I shall nonetheless thank you for spending your Friday on this!
Hmm, do you have a xorg.conf file lying around somewhere, the message about the xserver not being able to find an entry for screen 0 does not make sense ...
Good catch, I actually had two files under "/etc/X11/xorg.conf.d/":
- "00-keyboard.conf", from package "systemd-229-13.fc24.x86_64", with
contents
# Read and parsed by systemd-localed. It's probably wise not to edit this file # manually too freely. Section "InputClass" Identifier "system-keyboard" MatchIsKeyboard "on" Option "XkbLayout" "us" EndSection
- "01-resolution.conf", which I had created, in order to set the
preferred display resolution:
Section "Screen" Identifier "Default Screen" Device "Default Device" Monitor "Default Monitor" EndSection
Section "Device" Identifier "Default Device" Driver "modesetting" EndSection
Section "Monitor" Identifier "Default Monitor" Option "PreferredMode" "640x480" # Option "PreferredMode" "1440x900" EndSection
I removed these files now, and repeated the test. Again, the X server wouldn't start, but I think the log file looks a bit different now. Attached.
Ah, ok so it seems that my initial analysis is wrong, the problem is not a re-occuring of the device getting identified as a GPU screen, libdrm sorta depends on bus-ids and the lack of one is causing the server to misbehave. I guess that even with a xorg.conf things will fail with the troublesome kernel version (might be worth trying).
Emil's analysis seems to be spot on. This does not seem easily fixable in userspace / does seem like a real regression as it even breaks things when specifying the device through xorg.conf (I or so I believe) which is something which uses to work ...
In order to check this hypothesis, I did the following:
- I downgraded my xorg-x11-server installation to the most recent
official F24 packages, that is, "1.18.4-4.fc24",
- I kept the kernel that I built exactly at the regressive commit
(a325725633c2)
- I modified "01-resolution.conf" (see it above in the context) like this:
Section "Device" Identifier "Default Device" Driver "modesetting" BusID "PCI:00:02:0" <------------ new option added EndSection
where BusID matches the B/D/F of the virtio-vga device from "lspci".
This setup (modulo the kernel of course) was known to work, but now the X server actually segfaults (apparently in the xf86PlatformDeviceCheckBusID() function). Please find the logfile attached.
(NB: this is unrelated to upstream commit de9ce6757c2e -- which the pristine FC24 build lacks -- because I don't set AutoAddGPU to "off" -- it is left at its default "on" value.)
Where is this upstream commit again - it shows as unknown for the kernel, xserver and libdrm ?
So my theory was a bit off - SetVersion is the one responsible to set the "BusID", as retrieved by drmGetBusID, regardless if drmOpen or open is used.
Here's a bit of a brain dump from the other day:
- The commit mentioned 'affects' the drmSetBusid/DRM_IOCTL_SET_UNIQUE
userspace codepaths.
- The latter itself is dri1/legacy (xserver hw/xfree86/dri/) which is
not functional for platform devices. The latter of which seems to be the case for virt-gpu based on the kernel module.
- The modesetting driver should/cannot reach the above xserver codepath
That said, it seems that (at least some) userspace expects a PCI device despite the kernel module 'advertising' itself as platform one :-\
With kernel commit a325725633c2 applied, the drmGetBusid() call in get_drm_info() [hw/xfree86/os-support/linux/lnx_platform.c] returns "virtio0".
Without kernel commit a325725633c2 in place, the same function call produces "pci:0000:00:02.0".
I think that the idea of kernel commit a325725633c2:
We already have a fallback in place to fill out the unique from dev->unique, which is set to something reasonable in drm_dev_alloc.
is inappropriate for virtio devices.
While it is true that "virtioN" is unique across the guest system, those identifiers are not stable.
# ls -1d /sys/devices/pci*/*/virtio* /sys/devices/pci0000:00/0000:00:02.0/virtio0 /sys/devices/pci0000:00/0000:00:03.0/virtio1 /sys/devices/pci0000:00/0000:00:05.0/virtio2 /sys/devices/pci0000:00/0000:00:06.0/virtio3 /sys/devices/pci0000:00/0000:00:09.0/virtio4
If you tweak the PCI addresses of other virtio devices on the QEMU command line, while keeping the PCI address of the virtio-vga device intact, the "virtioN" identifier of the virtio-vga device may change in an unspecified / unexpected manner.
From the above listing, it seems like higher PCI Device numbers happen
to end up with higher "virtioN" identifiers. While this is unspecified / non-guaranteed behavior, in practice it means the following:
Moving the "virtio1" device from PCI address 00:03.0 to 00:01.0, while preserving the PCI address of virtio-vga as 00:02.0, will bump virtio-vga to "virtio1" from "virtio0" (and sink that other device from "virtio1" to "virtio0").
I think that unstable identifiers don't qualify for BusID use, regardless of the actual format of the IDs in question.
Searching the patch quickly, drm_virtio_set_busid() is the only implementation of the "drm_driver.set_busid" callback that delegates the task to drm_pci_set_busid(). All other implementations of this callback were provided by drm_platform_set_busid().
drm_platform_set_busid() would ultimately format "dev->platformdev->name" and "dev->platformdev->id" into the bus identifier. Replacing that common logic with the drm_dev_alloc() fallback that is already in place is probably justified: judging from "virtio0", the fallback likely captures the exact same information, just with a different format.
However, drm_virtio_set_busid() used to implement a different logic (encoding different information). It intentionally used stable PCI addresses rather than (platformdev->name, platformdev->id).
So, I think that removing drm_virtio_set_busid() was an actual regression. I propose that the related hunks of a325725633c2 be reverted. For virtio-vga and virtio-gpu-pci, "virtioN" is an unstable and inappropraite BusID pattern.
Thanks Laszlo